This invention is directed to the valve or other flow device connector art. More particularly the invention pertains to a connection nut which is fitted to a valve body of a valve used in ultra-high purity valve applications, after the valve body has been machined, after the valve internals have been assembled therein, and after substantially all of the in-process cleaning procedures have been performed.
Current practice in the use of a vacuum face seal for ultra-high-purity gas piping applications is to sandwich a thin metal gasket such as a soft nickel washer between the two machined faces of a coupling to be joined, and to threadedly drive the faces together, thus compressing the gasket and effecting a vacuum-tight seal. The compression is obtained by torquing a specially dimensioned nut on the female side against male threads that are either integral with, or slip over the piping on, the male side. Furthermore, in order to accommodate installation and maintenance requirements, the nut must translate far enough to expose the face seal for installation purposes.
The current standard configuration is the so-called "VCR type" nut or end fittings shown in side view in U.S. Pat. No. 4,634,099 and illustrated in cross-section in FIG. 1 herein. In prior art FIG. 1, a circular nut 11 having exterior hexagon flats 12 thereon and internal threads 14 in one end is first inserted over a narrow tube stub 15 of an outlet or inlet tube 16. An internal end flange 17 of the nut 11 abuts a distal flange 18 on the stub 15 with the interior threads 14 of the nut extending beyond the outer seal face 19 of the stub. The stub is then welded by bead 23 to the valve body 10 such as a valve body confining a bellows valve as seen in the above patent and in the related application. When a connecting tube 21 is to be assembled to the nut, gasket 20 is first placed in the nut to abut the seal face 19. The connecting tube 21 is placed so that its end face 22 is in abutment with the gasket 20 and upon being threaded-up by rotation of the nut, the gasket 20 is compressed between the abutting seal faces 19 and 22. A conventional leak test orifice 25 is also present in nut 11. The VCR nut does have a major disadvantage. Since the minimum inside diameter of the nut is less than the maximum outside diameter of the "VCR type" fitting, and must indeed be designed in such a manner to apply compression through the gasket, it must be slipped over the fitting prior to installing the fitting in the piping system.
While this may not be a major concern in standard piping configurations, it does become a problem in ultra-high purity valve applications. Generally speaking, the valve body must be processed independent of the fittings, and then the fittings welded onto the body as a final operation. The disadvantage here is that the user is left with several weld beads in the system that are not mechanically cleaned up and are detrimental to the gas system. Alternatively, the fittings could be welded to the valve body relatively early in the machining process, and the welds cleaned up as part of that process. In this case, the nuts are carried along with the valve body throughout the remainder of the machining process, where they are subjected to the effects of handling and processing that they would not otherwise be subjected to. This also precludes the use of any platings or coatings as an option, since these would be stripped off during any of several post-machining processes. Additionally, the presence of the nuts on the valve body complicates and can interfere with in-process cleaning procedures.